Polarizing plate and optical display including the same

Abstract

The present application discloses a polarizing plate and an optical display including the polarizing plate. The polarizing plate includes: a polarizer; and a first protective layer and a second protective layer sequentially stacked on one surface of the polarizer, wherein the second protective layer includes a positive C retardation layer having a thickness of about 10 μm or less, a refractive index of about 1.50 to about 1.55, and a glass transition temperature (Tg) of about 150° C. to about 250° C.

Description

[0001] Citations of Related Applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0125258 filed on September 25, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a polarizing plate and an optical display including the polarizing plate. Background Art

[0004] In recent years, as the trend toward thickness reduction of polarizing plates has increased, various attempts have been made to develop a retardation film including a base film and a coating layer by coating a coating composition on the base film, rather than bonding the two films via an adhesive layer.

[0005] As one of the liquid crystal displays, there is an in-plane switching (IPS) mode liquid crystal display. In the IPS mode liquid crystal display, nematic liquid crystals that are uniformly arranged and not applied with an electric field are driven by applying a lateral electric field to display an image. The IPS mode liquid crystal display has the advantage of a wider viewing angle than liquid crystal displays of other driving modes.

[0006] IPS mode liquid crystal displays have the problem that the color of the image changes significantly with the change of viewing angle (also known as lateral color shift). Various attempts have been made to overcome the color change of the image by viewing angle compensation and several optical compensation films. However, these technologies do not provide sufficient improvement in color change. In recent years, as the thickness of liquid crystal displays decreases and the size increases, the color change of the image becomes more obvious. Therefore, there is a need for an IPS mode liquid crystal display having a reduced thickness and a large area while ensuring good effects.

[0007] The background art of the present invention is disclosed in Japanese Unexamined Patent Publication No. JP2006-251659A and the like. Summary of the invention

[0008] One aspect of the present invention is to provide a polarizing plate including a positive C retardation layer having a thin thickness.

[0009] Another aspect of the present invention is to provide a polarizing plate including a positive C retardation layer to improve reliability and brightness.

[0010] One aspect of the present invention relates to a polarizing plate.

[0011] 1. The polarizing plate comprises: a polarizer; and a first protective layer and a second protective layer sequentially stacked on a surface of the polarizer, wherein the second protective layer comprises a positive C retardation layer having a thickness of about 10 μm or less, a refractive index of about 1.50 to about 1.55, and a glass transition temperature (Tg) of about 150 to about 250°C.

[0012] 2. In 1, the refractive index difference between the positive C retardation layer and the first protective layer may be about 0.1 or less.

[0013] 3. In 1 and 2, the refractive index difference between the positive C retardation layer and the polarizer may be about 0.05 or less.

[0014] 4. In 1-3, the positive C retardation layer can be a non-liquid crystal layer.

[0015] 5. In 1-4, the positive C retardation layer may contain at least one selected from cellulose ester compounds or polymers thereof and aromatic compounds or polymers thereof.

[0016] 6. In 5, the aromatic compound may include a polystyrene compound.

[0017] 7. In 6, the polystyrene compound may contain halogen.

[0018] 8. In 1-7, the positive C retardation layer may have an out-of-plane retardation of about -180 nm to about 0 nm and an in-plane retardation of about 0 nm to about 10 nm at a wavelength of about 550 nm.

[0019] 9. In 1-8, the stacked body of the first protective layer and the second protective layer may satisfy at least one of Relational Formulas 5 and 6:

[0020] [Equation 5]

[0021] Re(450) / Re(550)>Re(650) / Re(550)

[0022] Here, Re(450), Re(550) and Re(650) represent the in-plane retardation (unit: nm) of the stacked body of the first protective layer and the second protective layer at wavelengths of approximately 450 nm, 550 nm and 650 nm, respectively.

[0023] [Equation 6]

[0024] |Rth(450)| / |Rth(550)|>|Rth(650)| / |Rth(550)|

[0025] Here, Rth(450), Rth(550), and Rth(650) represent out-of-plane retardation (unit: nm) of the stack of the first protective layer and the second protective layer at wavelengths of approximately 450 nm, 550 nm, and 650 nm, respectively.

[0026] 10. In 9, the stack of the first protective layer and the second protective layer may have Re(450) / Re(550) of about 0.1 to about 10 and Re(650) / Re(550) of about 0.1 to about 5.

[0027] 11. In 9, the stack of the first protective layer and the second protective layer may have |Rth(450)| / |Rth(550)| of about 0.1 to about 10 and |Rth(650)| / |Rth(550)| of about 0.1 to about 5.

[0028] 12. In 1-11, the stacked body of the first protective layer and the second protective layer may satisfy relational expression 7:

[0029] [Equation 7]

[0030] Rth(550) / Re(550)≤-50

[0031] wherein Rth(550) represents the out-of-plane retardation of the stack of the first protective layer and the second protective layer at a wavelength of about 550 nm (unit: nm), and

[0032] Re(550) represents the in-plane retardation of the stacked body of the first protective layer and the second protective layer at a wavelength of about 550 nm (unit: nm).

[0033] 13. In 1-12, the first protective layer may have an in-plane retardation of about 10 nm or less and an out-of-plane retardation of about -10 nm to about 10 nm at a wavelength of about 550 nm.

[0034] 14. In 1-13, the first protective layer may include a cellulose ester resin film.

[0035] 15. In 1-14, the first protective layer and the second protective layer may be sequentially stacked on one surface of the polarizer or the second protective layer and the first protective layer may be sequentially stacked on one surface of the polarizer in the stated order.

[0036] 16. In 1-15, the polarizing plate may further include a third protective layer on the other surface of the polarizer.

[0037] 17. In 16, the third protective layer may have an in-plane retardation of about 5,000 nm or more at a wavelength of about 550 nm.

[0038] 18. In 1-17, the stack of the first protective layer and the second protective layer may have an out-of-plane retardation variation rate of about -15% to 0%, which is calculated by Equation 1:

[0039] Out-of-plane retardation change rate = [(AB) / B] × 100---------------------------------(Equation 1)

[0040] Wherein B represents the initial out-of-plane retardation of the stack of the first protective layer and the second protective layer at a wavelength of about 550 nm (unit: nm), and A represents the out-of-plane retardation of the stack of the first protective layer and the second protective layer at a wavelength of about 550 nm after being placed at about 60° C. and about 95% RH (relative humidity) for about 250 hours (unit: nm).

[0041] 19. In 1-18, the polarizing plate may have a machine (MD) shrinkage of about -0.48% to 0%, which is calculated by Equation 2:

[0042] MD shrinkage = [(CD) / D] × 100----------------------------------------(Equation 2)

[0043] Where D represents the initial MD length of the polarizing plate (unit: mm), and

[0044] C represents the MD length (unit: mm) of the polarizing plate after the polarizing plate is left at about 85° C. for about 24 hours.

[0045] 20. In 1-19, the polarizing plate may further include a fourth protective layer. The fourth protective layer may include a positive A retardation layer.

[0046] Another aspect of the invention relates to an optical display.

[0047] An optical display includes the polarizing plate according to the present invention.

[0048] The present invention provides a polarizing plate including a positive C retardation layer having a thin thickness.

[0049] The present invention provides a polarizing plate including a positive C retardation layer for improving reliability and brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention. DETAILED DESCRIPTION

[0051] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can thoroughly understand the present invention. It should be understood that the present invention can be implemented in different ways and is not limited to the following embodiments.

[0052] In the drawings, in order to clearly describe the present invention, components irrelevant to the description are omitted, and the same components will be represented by the same reference numerals throughout the specification. Although the length, thickness or width of each component may be exaggerated for understanding in the drawings, the present invention is not limited thereto.

[0053] Herein, spatially relative terms, such as "upper" and "lower", are defined with reference to the accompanying drawings. Thus, it should be understood that the term "upper surface" may be used interchangeably with the term "lower surface", and when an element, such as a layer or film, is referred to as being placed "on" another element, it may be placed directly on the other element or there may be intervening elements. On the other hand, when an element is referred to as being "directly placed on," "directly formed on," or "formed to be in direct contact with" another element, there are no intervening elements between them.

[0054] Herein, "in-plane retardation Re", "out-of-plane retardation Rth" and "biaxiality NZ" are represented by equations A, B and C, respectively:

[0055] Re=(nx-ny)×d,---(Equation A)

[0056] Rth=((nx+ny) / 2-nz)×d,---(Equation B)

[0057] NZ=(nx-nz) / (nx-ny), ---(Equation C)

[0058] Where nx, ny, nz are the refractive indices of the corresponding optical device in the slow axis direction, the fast axis direction and the thickness direction at the measurement wavelength, respectively, and d is its thickness (unit: nm). In equation AC, the measurement wavelength can be about 450 nm, about 550 nm and / or about 650 nm.

[0059] Herein, the x-axis direction is defined as the slow axis direction of the optical device, and the y-axis direction is defined as the fast axis direction thereof. The optical device may be a positive C retardation layer, a base layer and / or a protective layer.

[0060] Herein, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0061] In this article, the front side and the lateral side respectively refer to, based on the horizontal direction, in the spherical coordinate system represented by (θ, φ), the front side refers to (0°, 0°); when the left endpoint is represented by (90°, 0°) and the right endpoint is represented by (90°, 180°), the lateral side refers to the area from (60°, 45°) to (60°, 135°) or the area from (45°, 45°) to (45°, 135°).

[0062] Herein, the “refractive index” may refer to a value measured at a wavelength of about 200 nm to about 800 nm, specifically, at a wavelength of about 550 nm.

[0063] Herein, the “glass transition temperature” may be a value measured with respect to the positive C phase difference layer in a thermogram using a thermal analyzer DSC 8000 (Perkin Elmer Co., Ltd.) by heating about 10 mg of the positive C retardation layer from about 20° C. to 300° C. at a temperature increase rate slope of about 10° C. / min.

[0064] As used herein to indicate a particular numerical range, the expression "X to Y" means "greater than or equal to X and less than or equal to Y."

[0065] The present invention provides a polarizing plate, which includes a positive C retardation layer with a thin thickness as a non-liquid crystal layer to improve the bending performance and reliability of a panel and improve the left-right color deviation and the contrast of the lateral side of the panel while maintaining the brightness of the front side thereof. When applied to an optical display, the polarizing plate of the present invention has good effects in thickness reduction, brightness improvement and reliability, and can improve the color deviation and the contrast of the lateral side, thereby improving the screen quality of the optical display.

[0066] Next, we will refer to Figure 1 A polarizing plate according to one embodiment of the present invention is described. Figure 1 is a cross-sectional view of a polarizing plate according to one embodiment of the present invention.

[0067] Reference Figure 1 The polarizing plate includes a polarizer 100, a first protective layer 200, a second protective layer 300, and a third protective layer 400. The third protective layer 400 is formed on the upper surface of the polarizer 100, and the first protective layer 200 and the second protective layer 300 are sequentially stacked on the lower surface of the polarizer 100.

[0068] Although Figure 1 Not shown, an adhesive layer or a bonding layer may be formed on the lower surface of the second protective layer 300 to bond the polarizing plate to the panel of the optical display.

[0069] In one embodiment, the upper surface of the polarizer may correspond to the light exit surface of the polarizer, and the lower surface of the polarizer may correspond to the light incident surface of the polarizer. That is, the light emitted from the panel and incident on the polarizing plate may pass through the second protective layer, the first protective layer, the polarizer, and the third protective layer.

[0070] First protective layer

[0071] The first protective layer 200 may be directly formed on the second protective layer 300 and may support the second protective layer. As described below, the second protective layer may be formed by coating a composition for a second protective layer, particularly a composition for a positive C retardation layer, on one surface of the first protective layer and then drying. Herein, the phrase "directly formed on" means that there is no intermediate adhesive layer or bonding layer between the first protective layer and the second protective layer.

[0072] The first protective layer 200 may be an optically transparent film. For example, the first protective layer may have a total light transmittance of about 90% or more, for example, a total light transmittance of about 90% to about 100%. Within this range, the first protective layer 200 does not affect light passing through the second protective layer.

[0073] The first protective layer 200 may include an optically anisotropic film or an optically isotropic film.

[0074] In one embodiment, the first protective layer may have an in-plane retardation of about 10 nm or less at a wavelength of about 550 nm, for example, an in-plane retardation of about 0 nm to about 10 nm. Within this range, the first protective layer 200 does not affect light passing through the positive C retardation layer.

[0075] In one embodiment, the first protective layer may have an out-of-plane delay of about -10 nm to about 10 nm (e.g., -10 nm, -9 nm, -8 nm, -7 nm, -6 nm, -5 nm, -4 nm, -3 nm, -2 nm, -1 nm, 0 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm) at a wavelength of about 550 nm, for example, an out-of-plane delay of 0 nm to about 5 nm. Within this range, the first protective layer does not affect the light entering the polarizer or the light passing through the positive C retardation layer.

[0076] The first protective layer 200 may include a stretched film or a non-stretched film. When forming the positive C retardation layer, the non-stretched film can minimize the influence on the shrinkage of the positive C retardation layer.

[0077] In one embodiment, the first protective layer may include at least one selected from cellulose ester resins including triacetyl cellulose, cyclic polyolefin (COP) resins including norbornene, amorphous cyclic polyolefins, etc., polycarbonate resins, polyester resins including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc., polyether sulfone resins, polysulfone resins, polyamide resins, polyimide resins, non-cyclic polyolefin resins, poly(meth)acrylate resins including poly(methyl methacrylate), etc., polyvinyl alcohol resins, polyvinyl chloride resins, polyvinylidene chloride resins and acrylic resins, but is not limited thereto.

[0078] Preferably, the first protective layer includes a cellulose ester resin film containing triacetyl cellulose, etc. When the positive C retardation layer is formed using the composition for the positive C retardation layer described below, the cellulose ester resin film may be used to improve adhesion of the first protective layer to the positive C retardation layer.

[0079] In one embodiment, the first protective layer may have a lower refractive index than the second protective layer and may have a refractive index of about 1.45 to about 1.50, for example, about 1.45 to less than 1.50, specifically, about 1.47 to about 1.49.

[0080] The first protective layer 200 may have a thickness of about 10 μm to about 200 μm, specifically, about 20 μm to about 80 μm. Within this range, the first protective layer 200 can be used for the polarizing plate.

[0081] Second protective layer

[0082] The second protective layer includes a positive C retardation layer. The positive C retardation layer is used to improve screen quality by reducing color shift on the lateral side in a liquid crystal display, especially an IPS or FFS mode liquid crystal display.

[0083] The positive C retardation layer refers to a layer satisfying the relationship: nz>nx≒ny, where nz, nx and ny are the refractive indices of the positive C plate layer in its slow axis direction, fast axis direction and thickness direction at a wavelength of 550nm, respectively.

[0084] The positive C retardation layer may have an out-of-plane retardation of about -180 nm to about 0 nm at a wavelength of about 550 nm, specifically about -150 nm to about 0 nm, more specifically about -150 nm to about -30 nm, and even more specifically about -120 nm to about -50 nm. Within this range, the second protective layer can improve screen quality by reducing color change on the lateral side.

[0085] The positive C retardation layer may have an in-plane retardation of about 0 nm to about 10 nm at a wavelength of about 550 nm, specifically, an in-plane retardation of about 0 nm to about 8 nm, about 0 nm to about 5 nm. Within this range, the positive C retardation layer does not affect light entering the retardation film or light passing through the positive C retardation layer.

[0086] The positive C retardation layer may be a non-liquid crystal layer that does not contain a liquid crystal polymer or a monomer that forms a liquid crystal polymer. Therefore, the positive C retardation layer does not have the above-mentioned problems caused by the liquid crystal layer.

[0087] The positive C retardation layer may have a thickness of about 10 μm or less. According to the present invention, unlike a typical retardation film made by solvent casting or the like, the positive C retardation layer may have the above-mentioned out-of-plane retardation with a thickness of about 10 μm or less and may be manufactured by coating. Within this range, the positive C retardation layer may achieve the above-mentioned out-of-plane retardation while being able to reduce the thickness of the polarizing plate. Specifically, the positive C retardation layer may have a thickness of greater than about 0 μm to about 10 μm or less, more specifically, a thickness of about 0.5 μm to about 10 μm.

[0088] The positive C retardation layer may have a glass transition temperature of about 150°C to about 250°C (e.g., 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C). According to the present invention, the positive C retardation layer may be formed of a non-liquid crystal material and have a glass transition temperature of about 150°C to about 250°C. Within this glass transition temperature range, the thin positive C retardation layer may improve the reliability of the polarizing plate. In this article, "reliability" means that the second protective layer or the stack of the first protective layer and the second protective layer has a small retardation change when it is placed under high temperature and high humidity conditions (about 60°C and about 95% RH) for a long time and has a small shrinkage rate at high temperature (about 85°C).

[0089] In one embodiment, the second protective layer, the positive C retardation layer, or the stack of the first protective layer and the second protective layer has an out-of-plane retardation variation of about -15% to about 0%, for example, about -10% to about 0%, which is calculated according to Equation 1:

[0090] Out-of-plane retardation change rate = [(AB) / B] × 100---------------------------(Equation 1)

[0091] wherein B represents the initial out-of-plane retardation of the second protective layer, the positive C retardation layer, or the stack of the first protective layer and the second protective layer at a wavelength of about 550 nm (unit: nm), and

[0092] A represents the out-of-plane retardation (unit: nm) at a wavelength of about 550 nm after the second protective layer, the positive C retardation layer, or the stack of the first protective layer and the second protective layer is left at about 60° C. and about 95% RH for about 250 hours.

[0093] Within this range, the polarizing plate can have high reliability.

[0094] In one embodiment, the polarizing plate may have an MD shrinkage of about -0.48% to about 0%, for example, an MD shrinkage of about -0.45% to about -0.35%, which is calculated according to Equation 2:

[0095] MD shrinkage = [(CD) / D] × 100-----------------------------------(Equation 2)

[0096] Where D represents the initial MD length of the polarizing plate (unit: mm), and

[0097] C represents the MD length (unit: mm) of the polarizing plate after the polarizing plate is left at about 85° C. for about 24 hours. Herein, the initial MD length refers to the length of the polarizing plate before the polarizing plate is left at about 85° C. for about 24 hours.

[0098] Within this range, the polarizing plate can exhibit good bending characteristics in terms of panel reliability.

[0099] Specifically, the positive C retardation layer may have a glass transition temperature of about 170° C. to about 230° C., for example, a glass transition temperature of about 180° C. to about 220° C. Within this range, the positive C retardation layer can be easily made while ensuring good dimensional stability. The adjustment of the glass transition temperature of the positive C retardation layer will now be described in detail.

[0100] According to the present invention, the positive C retardation layer is formed of a non-liquid crystal polymer and the refractive index of the positive C retardation layer is controlled to be about 1.50-about 1.55 (e.g., 1.5, 1.51, 1.52, 1.53, 1.54 or 1.55) to improve brightness. Within this range, the positive C retardation layer can prevent interference patterns from being generated between layers by reducing the refractive index difference between the second protective layer and the polarizer when light passes through the second protective layer, the first protective layer and the polarizer, while improving light extraction efficiency without brightness loss. The method for adjusting the refractive index of the positive C retardation layer will now be described in detail.

[0101] Specifically, the positive C retardation layer may have a refractive index of about 1.50 to about 1.53.

[0102] In one embodiment, the refractive index difference between the second protective layer (specifically, the positive C retardation layer) and the first protective layer can be about 0.1 or less, for example, about 0 to about 0.06. Within this range, the polarizing plate can prevent the brightness loss of light emitted from the optical display. In one embodiment, the first protective layer can have a refractive index that is the same as or smaller than the refractive index of the second protective layer (specifically, the positive C retardation layer).

[0103] In one embodiment, the refractive index difference between the second protective layer (specifically, the positive C retardation layer) and the polarizer can be about 0.05 or less, for example, about 0 to about 0.02. Within this range, the polarizing plate can prevent the brightness loss of light emitted from the optical display. In one embodiment, the polarizer can have a refractive index that is the same as or greater than the second protective layer (specifically, the positive C retardation layer).

[0104] The positive C retardation layer may be formed of a composition for a positive C retardation layer.

[0105] The composition for the positive C retardation layer comprises at least one selected from cellulose ester compounds or polymers thereof and aromatic compounds or polymers thereof. In one embodiment, the positive C retardation layer comprises at least one selected from cellulose ester compounds or polymers thereof and aromatic compounds or polymers thereof. At least one selected from cellulose ester compounds or polymers thereof and aromatic compounds or polymers thereof can form a positive C retardation layer while easily satisfying the above-mentioned glass transition temperature and refractive index.

[0106] Next, the cellulose ester compound will be described.

[0107] The cellulose ester compound may include at least one selected from the group consisting of a cellulose ester resin, a cellulose ester oligomer, and a cellulose ester monomer.

[0108] The cellulose ester compound may include a condensation product obtained by a reaction between a hydroxyl group on cellulose ester and a carboxylic acid or a carboxylic anhydride.

[0109] The cellulose ester compounds may be regioselective or randomly substituted. Regioselectivity may be measured by determining the relative degrees of substitution at the C6, C3, and C2 positions on the cellulose ester using carbon 13 NMR. The cellulose ester compounds may be prepared by a typical process wherein a cellulose solution is contacted with at least one C1 to C20 acylating agent for a sufficient time to provide a cellulose ester having a desired degree of substitution and a desired degree of polymerization.

[0110] Preferably, the acylating agent comprises at least one linear or branched C1-C 20Alkyl or aryl carboxylic acid anhydride, acyl halide, diketone or acetoacetate. The example of carboxylic acid anhydride can include acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, caproic anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, substituted benzoic anhydride, phthalic anhydride and isophthalic anhydride. The example of acyl halide can include acetyl chloride, propionyl chloride, butyryl chloride, caproyl chloride, 2-ethylhexanoyl chloride, lauroyl chloride, palmitoyl chloride, benzoyl chloride, substituted benzoyl chloride and stearic anhydride. The example of acetoacetate can include methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate and tert-butyl acetoacetate. Most preferably, acylating agent includes straight or branched C2-C9 alkyl carboxylic acid anhydride, such as acetic anhydride, propionic anhydride, butyric anhydride, 2-ethylhexanoic anhydride, nonanoic anhydride and stearic anhydride.

[0111] Preferably, the cellulose ester compound includes, for example, cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB), but is not limited thereto.

[0112] In one embodiment, the cellulose ester compound may contain at least two acyl substituents. At least one acyl group may include an aromatic substituent, and in the cellulose ester compound, the relative degree of substitution (RDS) may be arranged in the order of C6>C2>C3. C6 represents the degree of substitution of the 6th carbon in the cellulose ester, C2 represents the degree of substitution of the 2nd carbon in the cellulose ester, and C3 represents the degree of substitution of the 3rd carbon in the cellulose. The aromatic compound may include benzoate or a substituted benzoate.

[0113] In another embodiment, the cellulose ester compound may include a regioselectively substituted cellulose ester compound having (a) a plurality of chromophore-acyl substituents and (b) a plurality of pivaloyl substituents.

[0114] The cellulose ester compound may have a hydroxyl degree of substitution of about 0.1 to about 1.2 and a chromophore-acyl degree of substitution of about 0.4 to about 1.6; the difference between the sum of the chromophore-acyl degree of substitution on the second carbon in the cellulose ester compound and the chromophore-acyl degree of substitution on the third carbon in the cellulose ester compound and the chromophore-acyl degree of substitution on the sixth carbon in the cellulose ester compound may be in the range of about 0.1 to about 1.6; and the chromophore-acyl group may be selected from (i), (ii), (iii) and (iv):

[0115] (i)(C6-C 20 ) aryl-acyl, wherein the aryl group is unsubstituted or substituted with 1-5 R 1 replace;

[0116] (ii) heteroaryl, wherein heteroaryl is a five- to ten-membered ring containing 1 to 4 heteroatoms selected from N, O and S, and is unsubstituted or substituted with 1 to 5 R1 replace;

[0117]

[0118] Where the aryl group is C6-C 20 Aryl, and is unsubstituted or substituted with 1-5 R 1 Replacement; and

[0119]

[0120] wherein heteroaryl is a five- to ten-membered ring containing 1-4 heteroatoms selected from N, O and S, and is unsubstituted or substituted with 1-5 R 1 replace,

[0121] R 1 are independently nitro, cyano, (C1-C6) alkyl, halo (C1-C6) alkyl, (C6-C 20 )Aryl-CO2-, (C6-C 20 )aryl, (C1-C6)alkoxy, halo(C1-C6)alkoxy, halogen, a five- to ten-membered heteroaryl group containing 1 to 4 heteroatoms selected from N, O and S, or

[0122]

[0123] In one embodiment, the chromophore-acyl group may be an unsubstituted or substituted benzoyl group, or an unsubstituted or substituted naphthyl group.

[0124] In one embodiment, the chromophore-acyl group may be selected from the group consisting of:

[0125]

[0126]

[0127]

[0128] Where * indicates the point of attachment of the chromophore-acyl substituent to the oxygen of the cellulose ester.

[0129] In another embodiment, the cellulose ester compound may include an ester polymer having an acyl unit, wherein at least some of the hydroxyl groups [C2 hydroxyl group, C3 hydroxyl group or C6 hydroxyl group] of the sugar monomer constituting the cellulose are unsubstituted or substituted, as shown in the following Formula 1:

[0130] [Formula 1]

[0131]

[0132] Wherein n is an integer of 1 or greater.

[0133] The substituents of the cellulose ester polymer or acyl unit may include halogen atoms, nitro groups, alkyl groups (e.g., C1-C 20 alkyl), alkenyl (e.g., C2-C 20 alkenyl), cycloalkyl (e.g., C3-C 10 Cycloalkyl), aryl (e.g., C6-C 20 aryl), heteroaryl (e.g., containing C3-C 10 carbon atoms), alkoxy (e.g., C1-C 20 The substituents may be the same as or different from each other.

[0134] In this context, "acyl" may refer to RC(=O)-* (* is the linking site, R is C1-C 20 Alkyl, C3-C 20 Cycloalkyl, C6-C 20 Aryl or C7-C 20 The "acyl" group is coupled to the cellulose ring via an ester bond (via an oxygen atom) in the cellulose.

[0135] Herein, for convenience, "alkyl", "alkenyl", "cycloalkyl", "aryl", "heteroaryl", "alkoxy" and "acyl" refer to non-halogen compounds. The composition for the second retardation layer may contain cellulose ester polymer alone or in a mixture thereof.

[0136] Herein, "halogen" refers to fluorine (F), Cl, Br or I, preferably F.

[0137] A "halogen-containing functional group" is an organic functional group containing at least one halogen atom, and may include aromatic, aliphatic or alicyclic functional groups. For example, the halogen-containing functional group may refer to a halogen-substituted C1-C 20 Alkyl, halogen substituted C2-C 20 Alkenyl, halogen substituted C2-C 20 Alkynyl, halogen substituted C3-C 10 Cycloalkyl, halogen substituted C1-C 20 Alkoxy, halogen-substituted acyl, halogen-substituted C6-C 20 Aryl or halogen substituted C7-C 20 Aralkyl, but not limited thereto.

[0138] "Halogen substituted acyl" can be R'-C(=O)-* (* is the attachment site, R' is a halogen substituted C1-C 20 Alkyl, halogen substituted C3-C 20 Cycloalkyl, halogen substituted C6-C 20Aryl or halogen substituted C7-C 20 The "halogen-substituted acyl group" can be coupled to the cellulose ring via an ester bond (via an oxygen atom) in cellulose.

[0139] Preferably, the composition of the positive C plate retardation layer includes a cellulose ester polymer substituted with an acyl group, a halogen or a halogen-containing functional group. More preferably, the halogen is fluorine. The halogen may be present in the cellulose ester polymer in an amount of 1 wt% to 10 wt%. Within this range, the composition allows for easy formation of a positive C plate retardation layer having the characteristics of the present invention and is capable of improving ellipticity.

[0140] In order to form the positive C plate retardation layer, the cellulose ester polymer may be prepared by a typical method known to those skilled in the art or may be obtained from a commercially available product. For example, a cellulose ester polymer having an acyl group as a substituent may be prepared by reacting trifluoroacetic acid or trifluoroacetic anhydride with a sugar monomer or a polymer of sugar monomers constituting cellulose represented by Formula 1; or by reacting trifluoroacetic acid or trifluoroacetic anhydride with a sugar monomer or a polymer of sugar monomers constituting cellulose represented by Formula 1, and then reacting an acylating agent (e.g., an anhydride of a carboxylic acid, or a carboxylic acid) therewith; or reacting both trifluoroacetic acid or trifluoroacetic anhydride and an acylating agent with a sugar monomer or a polymer of sugar monomers constituting cellulose represented by Formula 1.

[0141] Next, the aromatic compounds are described.

[0142] The aromatic compound includes a phenyl group and may include a polystyrene compound or a fluorobenzene or difluorobenzene structure, but is not limited thereto. In one embodiment, the polystyrene compound may include a moiety represented by Formula 2:

[0143] [Formula 2]

[0144]

[0145] in is the linking site of an atom,

[0146] R 1 , R 2 and R 3 are each independently a hydrogen atom, an alkyl group, a substituted alkyl group or a halogen;

[0147] R is each independently a substituent on the styrene ring; and

[0148] n is an integer of 0 to 5, indicating the number of substituents on the styrene ring.

[0149] Examples of the substituent R on the styrene ring can include alkyl, substituted alkyl, halogen, hydroxyl, carboxyl, nitro, alkoxy, amino, sulfonic acid, phosphoric acid, acyl, acyloxy, phenyl, alkoxycarbonyl and cyano. Herein, the "substituted" in "substituted alkyl" means that a hydrogen atom is substituted by any of these substituents.

[0150] In one embodiment, R 1 , R 2 and R 3 At least one of them may be halogen, preferably fluorine.

[0151] The composition of the positive C retardation layer may further include a solvent. The solvent may include at least one organic solvent selected from propylene glycol methyl ether, propylene glycol methyl ether acetate (PGMEA), methyl isopropyl ketone, methyl isobutyl ketone, toluene, xylene, methyl ethyl ketone, methanol, ethyl acetate, dichloromethane, cyclopentanone, tetrahydrofuran and methyl tert-butyl ether, but is not limited thereto.

[0152] The composition of the positive C retardation layer may further include an aromatic condensed ring-containing compound.

[0153] The aromatic condensed ring-containing compound is used to adjust the out-of-plane retardation and wavelength dispersion of the positive C retardation layer. The aromatic condensed ring-containing compound includes naphthalene, anthracene, phenanthrene, pyrene, the compound represented by structure 1 or the compound represented by structure 2. The aromatic condensed ring-containing compound may include 2-naphthyl benzoate, 2,6-naphthalene dicarboxylic acid diester represented by structure 3, naphthalene and absin acid ester represented by structure 4, but is not limited thereto:

[0154] [Structure 1]

[0155]

[0156] [Structure 2]

[0157]

[0158] [Structure 3]

[0159]

[0160] Where R is C1-C 20 Alkyl or C6-C 20 Aryl, n is an integer of 0-6.

[0161] [Structure 4]

[0162]

[0163] Where R is C1-C 20 Alkyl or C6-C 20 Aryl.

[0164] Preferably, the aromatic fused ring-containing additive includes at least one selected from naphthalene, anthracene, phenanthrene, pyrene, 2-naphthyl benzoate and the 2,6-naphthalene dicarboxylic acid diester represented by Structure 3.

[0165] In the positive C retardation layer, the additive containing an aromatic condensed ring may optionally be present in an amount of about 30 wt % or less, specifically about 0.1 wt % to about 30 wt %, preferably, about 10 wt % to about 30 wt %. Within this range, the additive can improve the thermal stability of the composition and the retardation per unit thickness of the polarizing plate, and can adjust the wavelength dispersion.

[0166] The composition for the positive C retardation layer may further include additives such as a plasticizer, a stabilizer, an ultraviolet absorber, an anti-blocking agent, a slip agent, a lubricant, a dye, a pigment, and a retardation enhancer, but is not limited thereto.

[0167] The positive C retardation layer can be formed by coating the composition for the positive C retardation layer on one surface of the first protective layer to a predetermined thickness to form a coating, and then heat curing the coating. Coating can be performed by typical methods known to those skilled in the art, for example, Meyer rod coating, die coating, etc. Thermal curing can include heat treating the coating at about 40°C to about 200°C, specifically about 60°C to about 150°C for about 1-10 minutes.

[0168] The glass transition temperature of the positive C retardation layer may be adjusted by, for example, heat-curing the coating layer of the positive C retardation layer after the coating layer is formed by coating.

[0169] The refractive index of the positive C retardation layer is adjusted by adjusting the solvent or the solvent content.

[0170] In one embodiment, the positive C retardation layer may satisfy at least one of equations 3 and 4:

[0171] [Equation 3]

[0172] Re(450) / Re(550)>Re(650) / Re(550)

[0173] Wherein Re(450), Re(550) and Re(650) represent the in-plane retardation of the positive C retardation layer at wavelengths of about 450 nm, 550 nm and 650 nm, respectively (unit: nm).

[0174] [Equation 4]

[0175] |Rth(450)| / |Rth(550)|>|Rth(650)| / |Rth(550)|

[0176] Wherein Rth(450), Rth(550) and Rth(650) represent the out-of-plane retardation of the positive C retardation layer at wavelengths of approximately 450 nm, 550 nm and 650 nm, respectively (unit: nm).

[0177] By satisfying at least one of Re and Rth defined in Relationships 3 and 4, the positive C retardation layer can help improve front contrast, lateral color shift, and black visibility.

[0178] Preferably, the positive C retardation layer further improves the front contrast, lateral color shift and black visibility by satisfying Relationship 4. More preferably, the positive C retardation layer further improves the front contrast, lateral color shift and black visibility by satisfying Relationships 3 and 4.

[0179] The positive C retardation layer may have Re(450) / Re(550) of about 0.1 to about 10, specifically about 0.5 to about 5, more specifically about 1 to about 3, and Re(650) / Re(550) of about 0.1 to about 5, specifically about 0.5 to about 3, more specifically about 0.1 to about 2. Within this range, Relationship 3 can be easily achieved.

[0180] In one embodiment, the positive C retardation layer may have Re(450) of about 0 nm to about 10 nm, specifically Re(450) of about 0 nm to about 7 nm, Re(550) of about 0 nm to about 10 nm, specifically Re(550) of about 0 nm to about 8 nm, more specifically Re(550) of about 0 nm to about 5 nm, and Re(650) of about 0 nm to about 6 nm, specifically Re(650) of about 0 nm to about 3 nm. Within this range, Relation 3 can be easily achieved.

[0181] The positive C retardation layer may have |Rth(450)| / |Rth(550)| of about 0.1 to about 10, specifically about 0.5 to about 5, more specifically about 1 to about 3.5, and even more specifically about 1 to about 3, and |Rth(650)| / |Rth(550)| of about 0.1 to about 5, specifically about 0.1 to about 3, and even more specifically about 0.1 to about 2. Within this range, Relationship 4 can be easily achieved.

[0182] In one embodiment, the positive C retardation layer may have an Rth(450) of about -200 nm to about 0 nm, specifically an Rth(450) of about -150 nm to about 0 nm, an Rth(550) of about -180 nm to about 0 nm, specifically an Rth(550) of about -150 nm to about 0 nm, more specifically an Rth(550) of about -150 nm to about -30 nm, more specifically an Rth(550) of about -150 nm to about -50 nm, and an Rth(650) of about -160 nm to about 0 nm, specifically an Rth(650) of about -130 nm to about 0 nm. Within this range, Relational Equation 4 can be easily achieved.

[0183] The positive C retardation layer of the relationship between equations 3 and 4 can be achieved by using the above-mentioned composition for the positive C retardation layer, and simultaneously adjusting at least one selected from the solvent type, solvent content, coating thickness and drying conditions.

[0184] In one embodiment, the stack of the first protective layer and the second protective layer (particularly, the positive C retardation layer) or the second protective layer may satisfy at least one of Relationships 5 and 6. Therefore, the stack can contribute to improving front contrast and lateral color shift.

[0185] [Equation 5]

[0186] Re(450) / Re(550)>Re(650) / Re(550)

[0187] Here, Re(450), Re(550) and Re(650) are the in-plane retardations (unit: nm) of the stack of the first protective layer and the second protective layer or the second protective layer at wavelengths of about 450 nm, about 550 nm and about 650 nm, respectively.

[0188] [Equation 6]

[0189] |Rth(450)| / |Rth(550)|>|Rth(650)| / |Rth(550)|

[0190] Here, Rth(450), Rth(550), and Rth(650) are out-of-plane retardations (unit: nm) of the stack of the first protective layer and the second protective layer or the second protective layer at wavelengths of about 450 nm, about 550 nm, and about 650 nm, respectively.

[0191] The stack of the first protective layer and the second protective layer or the second protective layer may have Re(450) / Re(550) of about 0.1 to about 10, specifically about 0.5 to about 5, more specifically about 1 to about 3, and Re(650) / Re(550) of about 0.1 to about 5, specifically about 0.1 to about 3, specifically about 0.5 to about 2. Within this range, Relational Formula 5 can be easily achieved.

[0192] In one embodiment, the stack of the first protective layer and the second protective layer or the second protective layer may have Re(450) of about 0 nm to about 10 nm, specifically Re(450) of about 0 nm to about 7 nm, Re(550) of about 0 nm to about 10 nm, specifically Re(550) of about 0 nm to about 8 nm, more specifically Re(550) of about 0 nm to about 5 nm, and Re(650) of about 0 nm to about 6 nm, specifically Re(650) of about 0 nm to about 3 nm. Within this range, Relational Equation 5 can be easily achieved.

[0193] The stack of the first protective layer and the second protective layer or the second protective layer may have |Rth(450)| / |Rth(550)| of about 0.1 to about 10, specifically about 0.5 to about 5, more specifically about 1 to about 3.5, and even more specifically about 1 to about 3 |Rth(450)| / |Rth(550)|, and |Rth(650)| / |Rth(550)| of about 0.1 to about 5, specifically about 0.1 to about 3, and even more specifically about 0.1 to about 2 |Rth(650)| / |Rth(550)|. Within this range, Relational Equation 6 can be easily achieved.

[0194] In one embodiment, the stack of the first protective layer and the second protective layer or the second protective layer can have an Rth(450) of about -200nm to about 0nm, specifically an Rth(450) of about -150nm to about 0nm, an Rth(550) of about -180nm to about 0nm, specifically an Rth(550) of about -150nm to about 0nm, more specifically an Rth(550) of about -150nm to about -30nm, more specifically an Rth(550) of about -150nm to about -50nm, and an Rth(650) of about -160nm to about 0nm, specifically an Rth(650) of about -130nm to about 0nm. Within this range, Relational Equation 6 can be easily achieved.

[0195] The stack of the first protective layer and the second protective layer or the second protective layer can be achieved by using the above-mentioned composition for a positive C retardation layer and adjusting at least one selected from the solvent type, solvent content, coating thickness and drying conditions.

[0196] The second protective layer (specifically, the positive C retardation layer) or the stack of the first protective layer and the second protective layer (specifically, the positive C retardation layer) can satisfy Relationship 7. The following relationship is the ratio of the out-of-plane retardation to the in-plane retardation and is a parameter representing the biaxiality of the birefringent layer. By satisfying the relationship, the polarizing plate can reduce the color shift in the optical display panel.

[0197] [Equation 7]

[0198] Rth(550) / Re(550)≤-50

[0199] wherein Rth(550) represents the out-of-plane retardation of the second protective layer (specifically, the positive C retardation layer) or the stack of the first protective layer and the second protective layer at a wavelength of about 550 nm (unit: nm), and

[0200] Re(550) represents the in-plane retardation of the second protective layer (specifically, the positive C retardation layer) or the stacked body of the first protective layer and the second protective layer at a wavelength of about 550 nm (unit: nm). Specifically, Rth(550) / Re(550) may be about -350 to about -50, specifically about -300 to about -50.

[0201] polarizer

[0202] The polarizer 100 is an absorption-type polarizer that splits incident light into two polarization components orthogonal to each other to transmit one polarization light component while absorbing the other polarization light component.

[0203] The polarizer 100 may have a transmittance of about 40% or more, specifically about 40% to about 45%. The polarizer may have a polarization degree of about 95% or more, specifically about 95% to about 100%, more specifically about 98% to about 100%. Within this range, the polarizer may further improve front contrast and durability.

[0204] The polarizer 100 may include a uniaxially stretched polarizer containing a dichroic dye. Specifically, the polarizer containing a dichroic dye may include a polarizer made by uniaxially stretching a base film for a polarizer in MD and then dyeing the base film with a dichroic dye (e.g., iodine or potassium iodide containing iodine). The base film of the polarizer may include a polyvinyl alcohol film or a derivative thereof, but is not limited thereto. The polarizer may be made by a typical method known to those skilled in the art.

[0205] The polarizer 100 may have a refractive index of about 1.50 or more, for example, about 1.50 to about 1.65, and more specifically, about 1.51 to about 1.64.

[0206] The polarizer 100 may have a thickness of about 1 μm to about 40 μm, specifically about 5 μm to about 30 μm, and more specifically about 10 μm to about 25 μm. Within this range, the polarizer may be used for a polarizing plate.

[0207] The third protective layer

[0208] The third protective layer 400 is disposed on the upper surface (light emitting surface) of the polarizer to protect the polarizer. The third protective layer can provide effects of improving front contrast, lateral color shift and black visibility by adjusting the interaxial angle as described below.

[0209] In one embodiment, the third protective layer may include an optically isotropic film.

[0210] In another embodiment, the third protective layer may include an optically anisotropic film.

[0211] The third protective layer 400 may have an axis with a high refractive index and an axis with a low refractive index in the in-plane direction. Herein, "axis with a high refractive index" and "axis with a low refractive index" are defined by comparing the refractive index between two axes in the in-plane direction of the third protective layer, i.e., the x-axis and its y-axis. Although not particularly limited, in the third protective layer, the axis with a high refractive index and the axis with a low refractive index in the in-plane direction may be formed by stretching during the manufacture of the protective layer. For example, the axis with a high refractive index may be a slow axis, and the axis with a low refractive index may be a fast axis. The third protective layer may include a TD uniaxially stretched protective film to have an axis with a low refractive index and an axis with a high refractive index in the in-plane direction.

[0212] Assuming that the axis with a high refractive index in the in-plane direction of the polarizer is the reference axis (0°), the angle range of the axis with a low refractive index relative to the reference axis in the in-plane direction of the third protective layer is about -5° to about +5°. Within this range, it is possible to achieve improvements in front contrast, lateral color shift, and black visibility. When used herein to represent angles, when 0° is used as the reference point, "+" represents the angle in the clockwise direction based on the reference point, and "-" represents the angle in the counterclockwise direction based on the reference point. In the in-plane direction of the polarizer, the axis with a high refractive index can correspond to the machine direction (MD) of the polarizer, and the axis with a low refractive index can correspond to the lateral direction (TD) of the polarizer.

[0213] In one embodiment, the third protective layer may have an in-plane retardation (Re) of about 5,000 nm or more at a wavelength of about 550 nm, specifically about 5,000 nm to about 15,000 nm, and more specifically about 5,000 nm to about 12,000 nm. Within this range, the third protective layer can improve the front contrast while suppressing the generation of rainbow spots. In one embodiment, the third protective layer may have an out-of-plane retardation (Rth) of about 6,000 nm or more at a wavelength of 550 nm, specifically about 6,000 nm to about 15,000 nm, and more specifically about 6,000 nm to about 12,000 nm. Within this range, the third protective layer can suppress the generation of spots caused by birefringence while ensuring an improved viewing angle of the liquid crystal display. In one embodiment, the third protective layer may have a biaxiality (NZ) of about 2.5 or less at a wavelength of 550 nm, specifically about 1.0 to about 2.2, more specifically about 1.2 to about 2.0, and most specifically about 1.4 to about 1.8. Within this range, the third protective layer can suppress the generation of spots due to birefringence while maintaining its mechanical strength.

[0214] In one embodiment, the third protective layer may include a film formed of a light-transmitting resin. For example, the third protective layer may include at least one selected from the following: cellulose ester resins, including triacetyl cellulose, etc.; cyclic polyolefin resins, including norbornene, amorphous cyclic polyolefins, etc.; polycarbonate resins; polyester resins, including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, etc.; polyether sulfone resins; polysulfone resins; polyamide resins; polyimide resins; non-cyclic polyolefin resins; poly(meth)acrylate resins, including polymethyl methacrylate, etc.; polyvinyl alcohol resins; polyvinyl chloride resins and polyvinylidene chloride resins, but are not limited thereto.

[0215] The third protective layer 400 may have a single-layer structure, or may include a laminate of single-layer resin films or a film formed by co-extrusion to integrate a plurality of layers.

[0216] In another embodiment, the third protective layer may be a protective coating layer. The protective coating layer may be formed of a typical composition known to those skilled in the art.

[0217] The third protective layer 400 may have a thickness of about 1 μm to about 100 μm, specifically about 5 μm to about 100 μm, specifically about 10 μm to about 90 μm, specifically about 15 μm to about 85 μm. Within this range, the third protective layer can be used for a polarizing plate.

[0218] Although Figure 1Although not shown, a functional coating such as a hard coating, an anti-fingerprint layer, an anti-reflection layer, etc. may also be formed on the upper surface of the third protective film 140. Figure 1 Not shown, the polarizer may be stacked on the third protective layer via an adhesive layer and / or a bonding layer.

[0219] Next, a polarizing plate according to another embodiment of the present invention will be described.

[0220] The polarizing plate according to the present embodiment is substantially the same as the polarizing plate of the above-described embodiments except for the stacking order of the third protective layer, the polarizer, the second protective layer, and the first protective layer in the present embodiment.

[0221] The third protection layer is stacked on the upper surface of the polarizer, and the second protection layer and the first protection layer are stacked in sequence on the lower surface of the polarizer.

[0222] An adhesive layer or bonding layer may be formed on the lower surface of the first protective layer to bond the polarizing plate to the panel of the optical display. In one embodiment, the upper surface of the polarizer may correspond to the light exit surface of the polarizer, and the lower surface of the polarizer may correspond to the light incident surface of the polarizer. That is, the light emitted from the panel and incident on the polarizing plate may pass through the first protective layer, the second protective layer, the polarizer, and the third protective layer.

[0223] The details of the polarizer, the first protective layer, the second protective layer, and the third protective layer according to the present embodiment are the same as those described above.

[0224] The polarizing plate according to the present invention may further include a fourth protective layer including a positive A retardation layer.

[0225] Next, a polarizing plate according to another embodiment will be described.

[0226] The polarizing plate of this embodiment includes a third protective layer, a polarizer, a first protective layer, a second protective layer, and a fourth protective layer, which are sequentially stacked in the order described, wherein the fourth protective layer may include a positive A retardation layer. Except for the fourth protective layer, the polarizing plate according to this embodiment is substantially the same as the aforementioned polarizing plate. Therefore, the following description will focus on the fourth protective layer.

[0227] The fourth protective layer may include a positive A retardation layer satisfying the following relationship: nx>ny≒nz, where nz, nx and ny are the refractive indices of the positive A plate layer in the slow axis direction, the fast axis direction and the thickness direction thereof at a wavelength of 550nm, respectively. Therefore, the polarizing plate can show further improvement in contrast and light leakage at opposite angles.

[0228] The fourth protective layer, specifically the positive A retardation layer, can have Re of 50 nm to about 200 nm, specifically Re of 70 nm to about 180 nm, and more specifically Re of 90 nm to about 150 nm at a wavelength of 550 nm. Within this range, the polarizing plate can show further improvements in contrast and light leakage at opposite angles.

[0229] The fourth protective layer, specifically the positive A retardation layer, may include at least one of a protective film, a protective coating and a liquid crystal panel.

[0230] The protective film may be formed of at least one selected from the following: cellulose resins, including triacetyl cellulose (TAC), etc.; polyester resins, including polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate (PEN), polybutylene naphthalate, etc.; cyclic polyolefin resins; polycarbonate resins; polyether sulfone resins; polysulfone resins; polyamide resins; polyimide resins; polyolefin resins; polyacrylate resins; polyvinyl alcohol resins; polyvinyl chloride resins and polyvinylidene chloride resins, but not limited thereto. Specifically, the protective film may be a TAC film or a PET film.

[0231] The protective coating layer may be formed of at least one selected from a heat-curable composition and a photocurable composition.

[0232] The liquid crystal panel allows the arrangement of liquid crystals to be changed according to an applied voltage, thereby enabling or disabling light emitted from a light source to pass through. The liquid crystal panel does not require a positive A retardation layer in an optical stack, thereby reducing the thickness of an optical display.

[0233] The liquid crystal panel may include a pair of substrates and a liquid crystal layer inserted between the pair of substrates and used as a display medium. One substrate (color filter substrate) is provided with a color filter and a black matrix, and the other substrate (active matrix substrate) is provided with a switching element (e.g., TFT) for controlling the electrical and optical properties of the liquid crystal, and a signal line and a pixel line for transmitting a gate signal to the switching element, but is not limited thereto.

[0234] In one embodiment, the liquid crystal panel may use an in-plane switching (IPS) mode liquid crystal. Therefore, the liquid crystal display can improve viewing angle characteristics.

[0235] The liquid crystal panel may have an in-plane retardation of 70 nm to about 180 nm, specifically, 90 nm to about 150 nm, at a wavelength of 550 nm.

[0236] The in-plane retardation of the liquid crystal panel at a wavelength of 550 nm can be controlled by adjusting the thickness of the liquid crystal layer in the liquid crystal panel.

[0237] The optical display according to the present invention includes the polarizing plate according to the present invention. In one embodiment, the optical display may include a light emitting diode display including an organic light emitting diode display, an IPS or FFS liquid crystal display, etc. In the optical display, the polarizing plate according to the present invention may be provided as an observer side polarizing plate or a light source side polarizing plate.

[0238] In one embodiment, the liquid crystal display includes a liquid crystal panel, a polarizing plate according to the present invention stacked on the light exiting surface of the liquid crystal panel (observer-side polarizing plate), and a polarizing plate stacked on the light incident surface of the liquid crystal panel (light source-side polarizing plate). The polarizing plate stacked on the light incident surface may include a typical polarizing plate known to those skilled in the art.

[0239] The liquid crystal display includes a light source on the lower surface of the polarizing plate on the light source side. The light source may include a light source having a continuous light emission spectrum. For example, the light source may include a white light LED (white LED) light source, a quantum dot (QD) light source, a metal fluoride red phosphor light source, specifically a KSF (K2SiF6:Mn 4+ ) phosphor or KTF(K2TiF6:Mn 4+ ) A light source of a phosphor, etc. The liquid crystal panel may be an IPS mode panel, but is not limited thereto.

[0240] Next, the present invention will be described in more detail with reference to Examples. However, it should be noted that these Examples are provided for illustration only and should not be construed in any way as limiting the present invention.

[0241] Example 1

[0242] The composition for the positive C retardation layer was prepared by mixing a polystyrene compound (including a fluorine-containing polystyrene unit, Eastman Co., Ltd.) and PGMEA. The positive C retardation layer (thickness: 5 μm, refractive index: 1.52, Tg: 213°C) was formed on the lower surface of a triacetylcellulose (TAC) film (KC4CT1W, thickness: 40 μm, Re: 0.10 nm, Rth: 0.30 nm, NZ: 0.8, refractive index: 1.48@550, Konica Co., Ltd.) by coating the prepared composition on the lower surface of the TAC film and then drying.

[0243] A polarizer (thickness: 17 μm, refractive index: 1.52) was made by uniaxially stretching a polyvinyl alcohol film (VF-TS#4500, thickness: 45 μm, Kuraray Co., Ltd.) on the MD of a polyvinyl alcohol film at 30°C to twice its initial value, then dyeing the stretched film with iodine, and stretching the dyed film in a boric acid aqueous solution at 60°C.

[0244] The upper surface of the TAC film is bonded to the lower surface (light incident surface) of the polarizer. The polarizing plate is made by bonding a polyethylene terephthalate (PET) film (thickness: 80 μm, Re: 8,500 nm, Rth: 9,300 nm, NZ: 1.55@550 nm, Toyobo Co., Ltd.) to the upper surface (light exit surface) of the polarizer.

[0245] In Table 1, the refractive index was measured by a refractometer (Prism Coupler, Metricon Co., Ltd.), and the Tg was measured using a thermal analyzer DSC 8000 (Perkin Elmer Co., Ltd.) by heating 10 mg of a positive C retardation layer from about 20°C to 300°C at a heating rate ramp of about 10°C / min, and using an AxoScan retardation tester to measure the retardation.

[0246] Embodiment 2-4

[0247] A retardation film and a polarizing plate were prepared in the same manner as in Example 1, except that the positive C retardation layer was changed as listed in Table 1.

[0248] Example 5

[0249] A polarizing plate was manufactured in the same manner as in Example 1, except that a positive A retardation layer was further formed on the lower surface of the positive C retardation layer.

[0250] Comparative Example 1

[0251] A polarizing plate was manufactured by laminating a TAC film, a polarizer, and a PET film in this order in the same manner as in Example 1, except that the positive C retardation layer was not formed.

[0252] Comparative Examples 2-5

[0253] A polarizing plate was prepared in the same manner as in Example 1, except that the positive C retardation layer was changed as listed in Table 1.

[0254] The properties listed in Table 1 were evaluated for the polarizing plates prepared in Examples and Comparative Examples.

[0255] (1) Equation 1 (unit: %): The out-of-plane retardation at a wavelength of 550 nm of the laminate of the TAC film and the positive C retardation layer in each Example and Comparative Example was measured. After the laminate was left at 60° C. and 95% RH for 250 hours, the out-of-plane retardation at a wavelength of 550 nm of the laminate was measured. Then, the value of Equation 1 was calculated.

[0256] (2) Equation 2 (unit: %): The polarizing plate prepared in each example and comparative example was cut into a rectangular sample (70 mm×70 mm, MD×TD). The sample was placed at 85° C. for 24 hours, and the MD length of the polarizing plate was measured. The value of Equation 2 was calculated.

[0257] (3) Brightness (unit: nit): A liquid crystal display (having the same configuration as that of FULL HD LED TV ADONIS (43", model: TS-430)) was manufactured except that the polarizing plate prepared in each of the Examples and Comparative Examples was used as an observer-side polarizing plate. The white brightness of the front side of the liquid crystal display was measured using a brightness tester EZCONTRAST X88RC (EZXL-176R-F422A4, ELDIM).

[0258] (4) Lateral color shift (△x, y, no unit): A liquid crystal display (having the same configuration as that of FULL HD LED TV ADONIS (43", model: TS-430)) was produced, except that the polarizing plate produced in each of the Examples and Comparative Examples was used as the observer-side polarizing plate. The color coordinates x and y at (45°, 45°) and (45°, 135°) were measured using a brightness tester EZCONTRAST X88RC (EZXL-176R-F422A4, ELDIM) as △x,y is calculated based on the color coordinates x and y of (45°, 45°) and (45°, 135°).

[0259] Table 1

[0260]

[0261] As shown in Table 1, the polarizing plate according to the present invention includes a positive C retardation layer having a thin thickness and satisfying Equations 1 and 2 to ensure good reliability and brightness improvement. In addition, although not shown in Table 1, the positive C retardation layer exhibits substantially the same level of retardation as the laminate.

[0262] In addition, although not shown in Table 1, the polarizing plate of Example 5 has a further improved effect compared with the polarizing plate of Example 1.

[0263] In contrast, the polarizing plates of Comparative Examples 2-5 fail to satisfy the refractive index according to the present invention and show less significant brightness improvement. In addition, the polarizing plates of Comparative Examples 2-5 fail to satisfy the glass transition temperature according to the present invention and Equations 1 and 2, thereby providing low reliability.

[0264] Although some embodiments have been described herein, it should be understood that various modifications, changes, variations, and equivalent embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A polarizing plate, comprising: polarizer; and a first protective layer and a second protective layer sequentially stacked on one surface of the polarizer, wherein the second protective layer comprises a positive C retardation layer, The positive C retardation layer has a thickness of 10 μm or less, a refractive index of 1.50 to 1.55, and a glass transition temperature of 170° C. to 230° C., The positive C retardation layer refers to a layer that satisfies the relationship: nz>nx≒ny, where nz, nx and ny are the refractive indices of the positive C plate layer in the slow axis direction, fast axis direction and thickness direction at a wavelength of 550nm, respectively. wherein the refractive index difference between the positive C retardation layer and the first protective layer is 0.1 or less, and Wherein the refractive index difference between the positive C retardation layer and the polarizer is 0.05 or less. 2 . The polarizing plate according to claim 1 , wherein the positive C retardation layer is a non-liquid crystal layer. 3 . The polarizing plate according to claim 1 , wherein the positive C retardation layer comprises at least one selected from the group consisting of a cellulose ester compound or a polymer thereof and an aromatic compound or a polymer thereof. The polarizing plate according to claim 3 , wherein the aromatic compound comprises a polystyrene compound. The polarizing plate according to claim 4 , wherein the polystyrene compound contains halogen. 6 . The polarizing plate of claim 1 , wherein the positive C retardation layer has an out-of-plane retardation of −180 nm to 0 nm and an in-plane retardation of 0 nm to 10 nm at a wavelength of about 550 nm.

7. The polarizing plate according to claim 1, wherein a stack of the first protective layer and the second protective layer satisfies at least one of Relational Formulas 5 and 6: [Equation 5] Re(450) / Re(550)>Re(650) / Re(550) Wherein Re(450), Re(550) and Re(650) represent the in-plane retardation of the stack of the first protective layer and the second protective layer at wavelengths of about 450 nm, 550 nm and 650 nm, respectively, and the unit is nm, [Equation 6] |Rth(450)| / |Rth(550)|>|Rth(650)| / |Rth(550)| Here, Rth(450), Rth(550) and Rth(650) represent the out-of-plane retardation of the stack of the first protective layer and the second protective layer at wavelengths of approximately 450 nm, 550 nm and 650 nm, respectively, and the unit is nm. 8 . The polarizing plate according to claim 7 , wherein a stack of the first protective layer and the second protective layer has Re(450) / Re(550) of 0.1 to 10 and Re(650) / Re(550) of 0.1 to 5. 9 . The polarizing plate according to claim 7 , wherein a stack of the first protective layer and the second protective layer has |Rth(450)| / |Rth(550)| of 0.1 to 10 and |Rth(650)| / |Rth(550)| of 0.1 to 5.

10. The polarizing plate according to claim 1, wherein the stack of the first protective layer and the second protective layer satisfies Relational Formula 7: [Equation 7] Rth(550) / Re(550)≤-50 wherein Rth(550) represents the out-of-plane retardation of the stack of the first protective layer and the second protective layer at a wavelength of about 550 nm, and its unit is nm, and Re(550) represents the in-plane retardation of the stacked body of the first protective layer and the second protective layer at a wavelength of about 550 nm, and its unit is nm. 11 . The polarizing plate of claim 1 , wherein the first protective layer has an in-plane retardation of 10 nm or less and an out-of-plane retardation of −10 nm to 10 nm at a wavelength of about 550 nm. 12 . The polarizing plate according to claim 1 , wherein the first protective layer comprises a cellulose ester resin film. 13 . The polarizing plate according to claim 1 , wherein the first protective layer and the second protective layer are sequentially stacked on one surface of the polarizer or the second protective layer and the first protective layer are sequentially stacked on one surface of the polarizer.

14. The polarizing plate according to claim 1, further comprising: A third protective layer is on the other surface of the polarizer. 15 . The polarizing plate of claim 14 , wherein the third protective layer has an in-plane retardation of 5,000 nm or more at a wavelength of about 550 nm.

16. The polarizing plate according to claim 1, wherein the stack of the first protective layer and the second protective layer has an out-of-plane retardation variation rate of -15% to 0%, which is calculated by Equation 1: [Equation 1] Out-of-plane retardation change rate = [(AB) / B] × 100 wherein B represents the initial out-of-plane retardation of the stack of the first protective layer and the second protective layer at a wavelength of about 550 nm, and its unit is nm, and A represents the out-of-plane retardation of the stacked body of the first protective layer and the second protective layer after being left at about 60° C. and about 95% RH for about 250 hours, and the unit is nm.

17. The polarizing plate according to claim 1, wherein the polarizing plate has an MD shrinkage of -0.48% to 0%, which is calculated by Equation 2: [Equation 2] MD shrinkage = [(CD) / D] × 100 Wherein D represents the initial MD length of the polarizing plate, and its unit is mm, and C represents the MD length of the polarizing plate after being placed at about 85° C. for about 24 hours, and its unit is mm, The initial MD length refers to the length of the polarizing plate before the polarizing plate is left at about 85° C. for about 24 hours.

18. The polarizing plate according to claim 1, further comprising: The fourth protective layer comprises a positive A retardation layer, and the positive A retardation layer satisfies the relationship: nx>ny≒nz, wherein nz, nx and ny are the refractive indices of the positive A plate layer in the slow axis direction, the fast axis direction and the thickness direction at a wavelength of 550nm respectively.

19. An optical display comprising the polarizing plate according to any one of claims 1 to 18.

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